Photodynamic Therapy (PDT) is a technique used to destroy cancerous cells using a photosensitizing drug activated by light. The preferred activation wavelength for the most studied drug, Photofrin, is 630 nm. Other, second-generation drugs, require laser sources at wavelengths between 630 - 1000 nm. Standard lasers can produce radiation in a subset of this range. The most common activation laser is a liquid dye laser pumped by either an Argon laser or a KTP laser. Both of these systems are large and consume substantial electrical power. Diode lasers have been proposed as PDT sources, but have limited tunability and presently produce insufficient power at many wavelengths of interest. This Phase II program will continue the work of the highly successful Phase I in developing a compact, robust, and efficient laser source optimized for PDT. This source is unique in that it can produce multiple watts of light over 600 - 1000 nm, making it compatible with most PDT drugs. No other laser source being considered for PDT has this capability. The source is based on a very efficient frequency converter. The goal of the Phase II program is to deliver a fully tested prototype for use in clinical work. PROPOSED COMMERCIAL APPLICATION The all-solid-state laser source developed in this program would lead to a more compact, reliable, electrically efficient, and wavelength diverse instrumentation for photodynamic therapy. This tunable source is capable of producing power at wavelengths not conveniently obtained by standard laser sources.